Today, along with an avalanche of the usual news of perfidy and perversion this world produces, was a note from the BBC describing some research at the University of Bath. In short: putting some stuff called Aqueous Cream BP on the skin of even healthy subjects is a bad idea. (Original article here.)
Aqueous Cream BP must be a British thing-- never seen it here. Apparently the manufacturers' original intent was for it to be used as a kind of gentle cleanser, to be washed off, but doctors started telling people with eczema that they should leave it on and use it as a moisturizer. It contains 1% w/v sodium lauryl sulfate, a detergent, and people, especially kids, have for years been complaining about it stinging. Big surprise: you shouldn't use it.
I'm not sure I buy the researchers' data on how this cream thins the stratum corneum--the topmost layer of skin--but they seem to show that when you start stripping off healthy skin that has been treated with the cream, its rate of water loss increases faster than that of untreated healthy skin. (The researchers' advanced tool for stratum corneum stripping: Scotch no. 845 book tape (St. Paul, MN, U.S.A.)
The authors say that most likely the detergent is breaking down lipids between cells in the stratum corneum, and making the skin more permeable.
This is cheap, easy research. It also proves something everyone already knew was true. So it's not the kind of work I propose to fund.
But it does let me ramble about moisturizers. I grew up in Canada, where doctors always prescribed Glaxal Base for my eczema. Let it be known: although Glaxal Base contains not a molecule of sodium lauryl sulfate, it completely sucks as a moisturizer. The best stuff I've found is Eucerin, or one of its generic analogs that you can find in CVS or Longs (but not Walgreens--their version is terrible). Eucerin, like a good mayonnaise, combines awesome greasiness with light fluffiness. OK, I'm exaggerating: it goes on like cream cheese. There's a science to moisturizers and Beiersdorf, the makers of Eucerin, have got it right.
No surprise, Beiersdorf is a German company. The Germans, in my personal experience, are a step ahead in eczema treatment.